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Divvela.Santhosh Raghava Rao, Sreevardhan cheerla / International Journal of Engineering

Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com

Vol. 3, Issue 2, March -April 2013, pp.1092-1097

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Signal Strength Enhancement Using Cellular Repeater On Three

Frequency Bands For Low Signal Coverage Areas

(GSM900, GSM 1800/DCS, 3G)

Divvela.Santhosh Raghava Rao[1] ,Sreevardhan cheerla[2] [1] B.tech ECE Final Year Student ,KL University, Guntur, Andhra Pradesh, India.

[2] Assistant Professor Dept.of ECE,KL university,Guntur,Andhrapradesh,India.

ABSTRACTThe intended application of our Cellular

Repeater is a system of duplex reception,

amplification and transmission used to enhance

uplink(UL) and downlink(DL) signals in areas of

low signal coverage i.e.; for the situations where

signal quality between the base station and the

receiver is poor and communication fails. This

will be helpful for cellular providers to rectify the

problems of poor signal service. This Tri-Band

Cellular Repeater consists of Bidirectional

amplifier, receiving and transmitting antennas.This paper discusses our assembling process,

beginning with component selection and our

difficulty in obtaining the required gain

according to the user requirement in the process

of testing. This cellular repeater can be operated

in 3 different operating frequency bands namely,

GSM 900, DCS and 3G. The operation of the

repeater can be switched between the three

bands depending on the user requirement using a

triplexer which provides proper switching among

the bands. This model helps a lot in providing

efficient signal service in the weaker coverageareas in the specified band of frequency.

Keywords: Bi-Directional Amplifier (BDA),

Yagi-Uda antenna, Patch panel antenna, power amplifier, GSM 900, DCS, 3G

IntroductionA Tri-band cellular repeater basically helps

the service provider to rectify the poor signal

service. It can be operated in three differentoperational frequencies according to the user’sconvenience and requirement. This cellular repeater is economical as all the components used are of lowcost and hence total cost has been integrated. It isuser-friendly and eco-friendly.

These are similar to the cellular broadcasttowers used by the network providers for broadcasting, but are much smaller in size and arerecommended to use for a particular building only.

Modern cellular repeater amplifiers rebroadcastcellular signals inside the building. The systemsusually use an external directional antenna to collect

the best cellular signal, which is then transmitted toan amplifier unit which amplifies the signal, and

retransmits it locally, providing significantlyimproved signal strength.

The more advanced models often alsoallow multiple cell phones to use the same repeater

at the same time, so are suitable for commercial aswell as home use. Yagi-Uda antenna will bemounted vertically at the roof top to the wall or pole

such that it receives the maximum signal from thenearest base station and the channel to channeldifference should be greater than 10db. Booster

should be protected from rain and moisture such thatit can give maximum radiations to patch panelantenna. The working of patch panel antenna is toradiate the amplified signal to various mobilestations. Indoor antenna should be kept at the weak coverage areas. The bandwidth specifications should be taken care as specified above. For indoor purpose

the gain should be not more the 70db, if gainexceeds the specifications it has to be controlled byManual gain control (MGC) and noise should not bemore than 6 db.

I. Methodology1. Different Operating Frequencies:

Repeaters are available for all the differentGSM frequency bands, some repeaters will handledifferent types of network such as multi-mode

GSM, DCS, 3G repeaters however dual- and tri- band systems cost significantly more. Repeater systems are available for certain Satellite phonesystems, allowing the satellite phones to be used

indoors without a clear line of sight to the satellite.

The frequency table for GSM, DCS, 3G:S.No. FrequencyBand

Uplink Frequency(MHz)

Downlink Frequency(MHz)

1 Global SystemFor MobileCommunications (GSM 900)

890-915MHz

935-960Mhz

2 Digital

Communication System(GSM 1800)

1710-1785

MHz

1805-

1880MHz

3 3r

Generation

(3G)

1920-

1980Mhz

2110-

2170Mhz

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2. External directional antenna (Yagi-Uda

Antenna):Although some of the less expensive

models do not include an external directionalantenna, they are crucial for providing significant

gain in signal strength. This is because of the

feasibility of antenna which can be oriented andlocated outside to provide the best possible signalavailable, usually aligned with the nearest cell

tower. Generally speaking the larger the externalantenna we locate the better the signal we receive-although even a small and correctly oriented

external antenna should provide better signal thanthe internal antenna on any cell phone. These caneither be fitted by professionals or will include asignal strength monitor for easy alignment.

3. Internal rebroadcast antenna (Patch Panel

Antenna):The better systems will generally include an internalmonopole antenna (although this type of antenna isfar from standardized) for rebroadcasting the signalinternally - the advantage of using a monopoleantenna is that the signal will be equally distributedin all directions (subject, of course, to attenuation

from obstacles). Because all radio antennas areintrinsically polarized, cell phones perform best

when their antennas are oriented parallel to the booster's antenna - although within reasonable

proximity the booster's signal will be strong enoughthat the orientation of the cell phone's antenna willnot make a significant difference in usability.

4. Bi-Directional Amplifier:

A basic Repeater mainly consists of Low noise

Amplifier, Band Pass filter, Power Amplifier andDuplex filters.The signal from the Yagi-Uda Antenna is guided to

the Duplex filter and is then directed to Low noiseAmplifier module.Low noise amplifier as a module is made up of

MGA 31589, Sawfilters and ABA54563. These arethe amplifiers which provide a sufficient amount of gain to the signal and are sent to the band pass filter.All these amplifiers are provided with biasing

components which include capacitors and inductors.Attenuation pads are provided to get the requiredamount of gain at each and every stage.

Signal from the Low Noise Amplifier (LNA) is sentto the Band Pass filter which selects the particular bandwidth in which the signal has to be amplified.The Bandwidth is selected as per the user

requirement in the three frequency bands (GSM,DCS, and 3G).Therequired signal is sent to the Power amplifier

module. This contains saw filters, ASL 19w andABA54563, Amplifier which amplifies the signal inthe required bandwidth. All the Amplifiers are

provided with the required biasing components. TheAmplified signal is given to the Duplex filter whichseparates out the low frequencies and highfrequencies and is given to the Mobile Server.

In Each and every module 220pf capacitors are placed in the RF path to block the DC voltage.When tested through a Network analyzer it should

not receive any DC voltage hence the 220pf capacitors are placed in the RF path.The Repeater is supplied with a 5V power supply.

Uplink and downlink frequency Response for GSM,

DCS and 3G are tested in the network analyzer andthe results obtained are mentioned below.

Duplex

filterLNA

Band pass

filter

Power

amplifier

Duplex

filter

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BLOCK DIAGRAM OF UPLINK:

BLOCK DIAGRAM OF DOWNLINK

III. CELLULAR REPEATER

INSTALLATION PROCEDURE:

Check Rx level, Receiving Quality and Channelto Channel power difference using cell phone,which has net monitor software. Thefollowing specifications have to be met at pick

up point.o Rx level: -60±10dBm.

o Receiving Quality: 0 to +3o Channel to Channel power difference : >7dB.

If the above parameters do not meet; then

change the pickup position, such that abovespecifications are met.

Fix Yagi-Uda antenna in vertical orientationtowards BTS direction, such that maximum Rxlevel is received.

Connect one end of the RF cable to Yagi-Udaantenna and other end to BTS/Yagi antenna

port of the Booster. Ensure that connections are proper and effective and avoid loose contacts.

Locate convenient place and position for booster and fix it. If it is outdoor installation,ensure that booster is protected from rain,moisture and dust.

Fix the power cord to the booster and connect

the PSU to the supply point.

Fix Patch antenna in vertical position, where the boosted signal is required. Ensure that Patch

antenna is fixed at least 2 meters away from the booster. Ensure that cables connected to the booster do not overlap each other.

Minimize cable length to avoid cable loss as far

as possible. Switch on the booster and adjust the manual

gain control if required.

Finally note down CID, CH & LAC.

IV. SIMULATIONS AND

DISCUSSIONS:

The Graphs mentioned below depict the gainobtained for uplink and downlink frequencies for theGSM 900, DCS/GSM 1800 and 3G frequency bands. The GSM, DCS and 3G are connected to atriplexer and we can operate all the three at a time or

individually as it depends upon the user requirement. All the three uplink frequencies can beobserved at a time and similarly all the three

downlink frequencies can be observed at a time onthe network analyzer screen. We can also observethe increase in bandwidth as the frequency of operation increases. Hence when GSM, DCS and3G are maintained at same gain we can observe that3G has more bandwidth when compared to DCSandGSM frequencies.

GSM 900 MHz Frequency Responses

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3G 2100 MHz Frequency ResponseDCS 1800Mhz Frequency Response

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TRI BAND (GSM 900, DCS, 3G) FREQUENCY

RESPONSE

Observations:

GSM UPLINK Gain59.489dB

Frequency Range 890MHz - 915MHz

GSM DOWN LINK Gain65.849dBFrequency Range935MHz - 960MHz

DCS UPLINK Gain 58.679dB

Frequency Range1710MHz – 1785MHz

DCS DOWNLINK Gain60.025dB

Frequency Range1805MHz – 1880 MHz

3G UPLINK Gain 59.611dB

Frequency Range 1920MHz – 1980MHz

3G DOWNLINK

Gain 65.287dBFrequency Range 2110MHz – 2170MHz

Performance of 3G:

Variation of the signal strength before and after

switching of the cellular repeater:When the cellular repeater is in OFF state

DOWNLINK

(Mb/s)

UPLINK

(Mb/s)

LATENCY

(ms)

0.31 0.1 57

0.45 0.12 45

0.66 0.28 80

When the cellular repeater is in ON state

DOWNLINK

(Mb/s)

UPLINK

(Mb/s)

LATENCY

(ms)

1.92 1.15 58

2.21 2.31 49

2.42 0.54 60

If we observe from above table, the amplification of

signal is almost seven times the normal signal.

Calculation of the final output gain:

By using the net monitor software the gainin the required channel and its neighbor channels can also be calculated.

Using that process the signal gain in a particular channel is obtained.

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Then the gain of the External Directionalantenna is added to that signal gain, to the

resultant gain the return loss of the cable isadded.

To that gain the Internal Rebroadcastantenna gain is added.

Finally the resultant gain gives the outputgain with which the weaker signal is

boosted to increase the signal service in the particular area.

ConclusionWe analyzed from our observations that

signal can be enhanced in low coverage areas withthe help of these boosters. We have observed the

amplifications of 3G speed when booster is ON andOFF. Hence, practically also proved the importanceof repeater in enhancing the signal. Finally, we

conclude by saying that repeaters can improve thesignal strength in low signal coverage areas to suchan extent that everyone can receive signals without

having any disturbances.

References:[1] K. V. S. Rao, P. V. Nikitin and S. Lam,

“Antenna design for UHF RFID tags: Areview and a practical application,” IEEETransactions on Antennas and

Propagation, vol. 53, no. 12, pp. 3870-3876, Dec. 2005.

[2] K.P. Ray and Y. Ranga, “CPW-fed

modified rectangular printed monopoleantenna with slot,” Microwave andOptoelectronicsConference, 2007 IMOC2007 SBMO/IEEE MTT-S International,

pp.79-81, Oct. 29 2007-Nov. 1 2007.[3] C. Balanis, Antenna Theory, Analysis and

Design, 3rd edition, New York: Wiley,

2005.[4] R. C. Baraniuk, V. Cevher, and M. B.

Wakin, “Low-dimensional models for dimensionality reduction and signal

recovery, a geometrical perspective,” Proc.

IEEE , vol. 98, no. 6, pp. 959 – 971,Jun.

2010.[5] O. M. Bucci, G. D’Elia, and M. D.Migliore, “A new strategy to reduce thetruncation error in near-field far-fieldtransformations,” Radio Sci.,vol. 35, no. 1, pp. 3 – 17, Jan. – Feb. 2000.

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